Generally, a secondary battery refers to a rechargeable battery, while a primary battery refers to a non-rechargeable battery. Secondary batteries are widely used for electronic devices such as cellular phones, notebook computers, video cameras, electric vehicles, or the like. In particular, a lithium secondary battery has an operating voltage of about 3.6 V, triple the capacity of nickel-cadmium batteries or nickel hydrogen batteries generally used as power sources of electronic devices, and due to its high energy density per unit weight, are being utilized more and more.
The lithium secondary battery generally uses lithium oxide and carbonaceous material as a cathode active material and an anode active material, respectively. The lithium secondary battery includes an electrode assembly in which a cathode plate and an anode plate respectively coated with the cathode active material and the anode active material are disposed with a separator interposed between them, and an exterior material which seals and receives the electrode assembly together with an electrolyte.
Meanwhile, depending on the shape of the battery case, a lithium secondary battery may be classified into a can type secondary battery where the electrode assembly is included in a metal can and a pouch type battery where the electrode assembly is included in a pouch of an aluminum laminate. In addition, depending on the shape of the metal can, the can type secondary battery may be further classified into a cylindrical battery and a rectangular battery. The exterior material of the rectangular or cylindrical secondary battery includes a battery can and a cap assembly sealably coupled to an open end of the battery can.
FIG. 1 is a sectional view showing a cap assembly 10 of a conventional cylindrical secondary battery.
Referring to FIG. 1, the cylindrical secondary battery generally includes a cylindrical battery can 20, a jelly-roll type electrode assembly 30 received in the battery can 20, a cap assembly 10 coupled to the upper portion of the battery can 20, a beading portion 40 provided at the front end of the battery can 20 for mounting the cap assembly 10, and a clamping portion 50 for sealing the battery.
The electrode assembly 30 is wound into a jelly-roll shape in a state where a separator is interposed between a cathode and an anode. A cathode lead 31 is attached to the cathode and connected to the cap assembly 10, and an anode lead (not shown) is attached to the anode and connected to the lower end of the battery can 20.
The cap assembly 10 includes a top cap 11 forming a cathode terminal, a safety element 12 for interrupting a current by increasing the resistance when the temperature in the battery increases, a safety vent 13 for interrupting a current and/or for exhausting gas when the pressure in the battery increases, an insulation member 14 for electrically separating a safety vent 13 except for a specific portion from a current interrupt member 15, and a current interrupt member 15 connected to a cathode lead 31 connected to the cathode, which are laminated in the above order. In addition, the cap assembly 10 is mounted to the beading portion 40 of the battery can 20 in a state of being mounted to a gasket. Therefore, in a normal operating condition, the cathode of the electrode assembly 30 is electrically connected to the top cap 11 via the cathode lead 31, the current interrupt member 15, the safety vent 13, and the safety element 12.
However, since the conventional secondary battery configured as above has the beading portion 40, the receiving space of the electrode assembly decreases as much as the area occupied by the beading portion 40, which may be an obstacle in increasing the capacity of the secondary battery.
Nevertheless, the beading portion 40 is provided at the secondary battery because if the beading portion 40 is not provided, the cap assembly 10 may not be easily placed on and coupled to the open end of the battery can 20. In addition, because it is difficult to ensure stable coupling force and sealing force of the cap assembly 10, problems such as power insensibility or electrolyte leakage may occur due to the separation of the cap assembly 10 or the cut of the electrode lead. Further, separation of the cap assembly 10 or electrolyte leakage may lead to secondary battery failure or damage or to even more serious problems such as fire or explosion.